Organic light-emitting display device and method of manufacturing the same

ABSTRACT

An organic light-emitting display device and a method of its manufacture are provided, whereby manufacturing processes are simplified and display quality may be enhanced. The display device includes: an active layer of a thin film transistor (TFT), on a substrate and including a semiconducting material; a lower electrode of a capacitor, on the substrate, doped with ion impurities, and including a semiconducting material; a first insulating layer on the substrate to cover the active layer and the lower electrode; a gate electrode of the TFT, on the first insulating layer; a pixel electrode on the first insulating layer; an upper electrode of the capacitor, on the first insulating layer; source and drain electrodes of the TFT, electrically connected to the active layer; an organic layer on the pixel electrode and including an organic emission layer; and a counter electrode facing the pixel electrode, the organic layer between the counter electrode and the pixel electrode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/069,346, filed Mar. 22, 2011, which claims priority to and thebenefit of Korean Patent Application No. 10-2010-0046030, filed on May17, 2010, the entire content of both of which is incorporated herein byreference.

BACKGROUND

1. Field

Aspects of embodiments according to the present invention relate to anorganic light-emitting display device and a method of manufacturing thesame.

2. Description of Related Art

Organic light-emitting display devices are expected to be the nextgeneration of display devices due to their light weight, narrow profile,wide viewing angle, short response time, and low power consumption. Anorganic light-emitting display device that implements full-color imagesmay employ an optical resonance structure that has different opticallengths at pixels with different colors (for example, red, green, andblue pixels).

SUMMARY

One or more embodiments of the present invention provide an organiclight-emitting display device that is manufactured in a simple processand has excellent display quality, and a method of manufacturing thesame.

In an exemplary embodiment according to the present invention, anorganic light-emitting display device is disclosed. The organiclight-emitting display device includes a substrate, an active layer of athin film transistor, a lower electrode of a capacitor, a firstinsulating layer, a gate electrode of the thin film transistor, a pixelelectrode, an upper electrode of the capacitor, source and drainelectrodes of the thin film transistor, an organic layer, and a counterelectrode. The active layer is on the substrate and includes asemiconducting material. The lower electrode is on the substrate, dopedwith ion impurities, and includes a semiconducting material. The firstinsulating layer is on the substrate and covers the active layer and thelower electrode. The gate electrode is on the first insulating layer andincludes first, second, and third gate electrodes that are sequentiallystacked. The first gate electrode includes a metal. The second gateelectrode includes a transparent conductive material. The third gateelectrode includes a metal. The pixel electrode is on the firstinsulating layer and includes first and second pixel electrodes that aresequentially stacked. The first pixel electrode includes a metal. Thesecond pixel electrode includes a transparent conductive material. Theupper electrode is on the first insulating layer and includes first andsecond upper electrodes. The first upper electrode includes a metal. Thesecond upper electrode includes a transparent conductive material. Thesource and drain electrodes are electrically connected to the activelayer. The organic layer is on the pixel electrode and includes anorganic emission layer. The counter electrode faces the pixel electrode.The organic layer is intervening between the counter electrode and thepixel electrode.

The first gate electrode, the first pixel electrode, and the first upperelectrode may each include a first metal. The first metal may be analuminum alloy.

The aluminum alloy may further include nickel.

The first metal may have a thickness in a range of 50 to 200 Å.

The second gate electrode, the second pixel electrode, and the secondupper electrode may each include a same transparent conductive material.The same transparent conductive material may include a material selectedfrom the group including indium tin oxide (ITO), indium zinc oxide(IZO), zinc oxide (ZnO), indium oxide (In₂O₃), indium gallium oxide(IGO), aluminum zinc oxide (AZO), and combinations thereof.

The organic light-emitting display device may further include a thirdpixel electrode and a second insulating layer. The third pixel electrodeis on the second pixel electrode and includes a metal. The secondinsulating layer is on the first insulating layer, covers the thirdpixel electrode and the gate electrode, and includes first, second, andthird openings. The first opening is for exposing a portion of thesecond pixel electrode. The second opening is for exposing a portion ofthe third pixel electrode. The third opening is for exposing the secondupper electrode. The source and drain electrodes may be formed on thesecond insulating layer. One of the source and drain electrodes maycontact the third pixel electrode via the second opening.

The third pixel electrode and the third gate electrode may each includea second metal. The second metal may include a metal selected from thegroup including aluminum (Al), platinum (Pt), palladium (Pd), silver(Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium(Ir), chromium (Cr), lithium (Li), calcium (Ca), molybdenum (Mo),titanium (Ti), tungsten (W), copper (Cu), and combinations thereof.

The third pixel electrode and the third gate electrode may each includemulti-layered metal layers.

The first pixel electrode may be a semi-transmissive mirror forpartially transmitting and partially reflecting light emitted from theorganic emission layer.

The counter electrode may be for reflecting light emitted from theorganic emission layer.

The etched surfaces on both sides of each of the first pixel electrodeand the second pixel electrode may be identical to each other.

The organic light-emitting display device may further include a thirdinsulating layer on the second insulating layer. The third insulatinglayer includes a fourth opening exposing a portion of the second pixelelectrode exposed via the first opening, and covers the source and drainelectrodes and the second upper electrode exposed via the third opening.

According to another exemplary embodiment of the present invention, amethod of manufacturing an organic light-emitting display device isdisclosed. The method includes performing first, second, third, fourth,and fifth mask processes. The first mask process is for forming asemiconductor layer on a substrate and patterning the semiconductorlayer as an active layer of a thin film transistor and a lower electrodeof a capacitor. The second mask process is for forming a firstinsulating layer on the substrate to cover the active layer and thelower electrode, sequentially stacking a first metal layer, a firsttransparent conductive layer, and a second metal layer on the firstinsulating layer, and then patterning the first metal layer, the firsttransparent conductive layer, and the second metal layer as a pixelelectrode, a gate electrode of a thin film transistor, and an upperelectrode of the capacitor. The pixel electrode includes first, second,and third pixel electrodes that are sequentially stacked. The gateelectrode includes first, second, and third gate electrodes that aresequentially stacked. The upper electrode includes first, second, andthird upper electrodes that are sequentially stacked. The third maskprocess is for forming a second insulating layer on the first insulatinglayer to cover the pixel electrode, the gate electrode, and the upperelectrode, and patterning the second insulating layer to have first,second, and third openings, and contact holes. The first and secondopenings expose the third pixel electrode. The contact holesrespectively expose source and drain regions of the active layer. Thethird opening exposes the third upper electrode. The fourth mask processis for forming a third metal layer on the second insulating layer tocover exposed portions via the first, second, and third openings and thecontact holes, and patterning the third metal layer as source and drainelectrodes. The fifth mask process is for forming a third insulatinglayer on the second insulating layer to cover the source and drainelectrodes, and patterning the third insulating layer to have a fourthopening exposing the pixel electrode.

After the performing of the second mask process, the method may furtherinclude doping the source and drain regions with ion impurities by usingthe first, second, and third gate electrodes as masks.

The performing of the fourth mask process may include removing a portionof the third pixel electrode exposed via the first opening and the thirdupper electrode exposed via the third opening.

The performing of the fourth mask process may include removing the thirdupper electrode exposed via the third opening. After the performing ofthe fourth mask process, the method may further include doping ionimpurities into the lower electrode from the second upper electrodeexposed via the third opening.

The first metal layer may include an aluminum alloy.

The aluminum alloy may further include nickel.

The first metal layer may have a thickness in a range of 50 to 200 Å.

The first transparent conductive layer may include a material selectedfrom the group including indium tin oxide (ITO), indium zinc oxide(IZO), zinc oxide (ZnO), indium oxide (In₂O₃), indium gallium oxide(IGO), aluminum zinc oxide (AZO), and combinations thereof.

The second metal layer may include a metal selected from the groupincluding aluminum (Al), platinum (Pt), palladium (Pd), silver (Ag),magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd), iridium (Ir),chromium (Cr), lithium (Li), calcium (Ca), molybdenum (Mo), titanium(Ti), tungsten (W), copper (Cu), and combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and aspects of the present invention willbecome more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIGS. 1 through 15 are schematic cross-sectional views sequentiallyillustrating a method of manufacturing an organic light-emitting displaydevice, according to an embodiment of the present invention; and

FIG. 16 is a schematic cross-sectional view of an organic light-emittingdisplay device manufactured using the method of FIGS. 1 through 15,according to an embodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Likereference numerals refer to like elements throughout.

An organic light-emitting display device according to an embodiment ofthe present invention and a method of manufacturing the same will bedescribed with reference to FIGS. 1 through 16. FIGS. 1 through 15 areschematic cross-sectional views sequentially illustrating a method ofmanufacturing an organic light-emitting display device, according to anembodiment of the present invention. FIG. 16 is a schematiccross-sectional view of an organic light-emitting display devicemanufactured using the method of FIGS. 1 through 15, according to anembodiment of the present invention.

Referring to FIG. 1, a buffer layer 11 and a semiconductor layer 12 aresequentially formed on a substrate 10. The substrate 10 may be formed ofa transparent glass material including SiO₂ as a main component.

The buffer layer 11 may be formed on the substrate 10 to provide thesubstrate 10 with a smooth surface and prevent impurity elements frompenetrating into the substrate 10. The buffer layer 11 may include SiO₂and/or SiN_(x) (x≧1). The buffer layer 11 and the semiconductor layer 12each may be deposited using any one of various deposition methods suchas plasma enhanced chemical vapor deposition (PECVD), atmosphericpressure CVD (APCVD), low pressure CVD (LPCVD), and the like.

The semiconductor layer 12 may be formed on the buffer layer 11. Thesemiconductor layer 12 may be formed of amorphous silicon orpolysilicon. In this regard, the polysilicon may be formed bycrystallizing amorphous silicon by rapid thermal annealing (RTA), solidphase crystallization (SPC), excimer laser annealing (ELA), metalinduced crystallization (MIC), metal induced lateral crystallization(MILC), sequential lateral solidification (SLS), or the like.

Referring to FIG. 2, a first photo-resist (P1) is coated on thesemiconductor layer 12, and a first photomask process is performedthereon using a first photomask M1 including a light-blocking portionM11 and a light-transmitting portion M12. Although not particularlyillustrated in FIG. 2, an exposure device is used to perform an exposingprocess using the first photomask M1, followed by a series of processessuch as developing, etching, and stripping or ashing.

Referring to FIG. 3, because of the first photomask process, thesemiconductor layer 12 is patterned as an active layer 212 of a thinfilm transistor and a lower electrode 312 of a capacitor. The lowerelectrode 312 of the capacitor is formed of the same material as that ofthe active layer 212 on the same layer on which the active layer 212 isformed.

Referring to FIG. 4, a first insulating layer 13, a first metal layer14, a first transparent conductive layer 15, and a second metal layer 16are sequentially stacked on the resulting structure of FIG. 3. The firstinsulating layer 13 may be formed as a single layer formed of SiO₂ orSiN_(x), or a plurality of layers formed of SiO₂ and SiN_(x), and actsas a gate-insulating layer of the thin film transistor and a dielectriclayer of the capacitor.

The first metal layer 14 may be formed of an aluminum alloy. Thealuminum alloy may include aluminum as a main component and may furtherinclude nickel (Ni). In addition, the aluminum alloy may further includea small amount of silicon (Si), lanthanum (La), germanium (Ge), and/orcobalt (Co). Since the first metal layer 14 is formed of an aluminumalloy, when the first metal layer 14, the first transparent conductivelayer 15, and the second metal layer 16 are etched, the second metallayer 16 and/or the first transparent conductive layer 15 may be etchedwithout damage. Thus, the manufacturing process of the organiclight-emitting display device may be enhanced. In addition, the firstmetal layer 14 may further include a small amount of Ni, thereby furtherenhancing etching properties, which results in further enhancing themanufacturing process of the organic light-emitting display device.Because of the etching process, the first metal layer 14, the firsttransparent conductive layer 15, and the second metal layer 16 have thesame (e.g., identical) etched surfaces on their sides (see, for example,FIG. 6).

The first metal layer 14 is formed as a semi-transmissive reflectivefilm, e.g., as a semi-transmissive mirror, and has a thickness of 50 to200 Å. In one embodiment, when the thickness of the first metal layer 14is less than 50 Å, the reflectance of the first metal layer 14 decreasessignificantly and thus, it is difficult to form optical resonancebetween the first metal layer 14 and a counter electrode, which will bedescribed later. In another embodiment, when the thickness of the firstmetal layer 14 is greater than 200 Å, the transmissivity of the firstmetal layer 14 decreases significantly and thus, the luminous efficiencyof an organic light-emitting display device decreases.

The first transparent conductive layer 15 may include indium tin oxide(ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In₂O₃),indium gallium oxide (IGO), and/or aluminum zinc oxide (AZO). The secondmetal layer 16 may include aluminum (Al), platinum (Pt), palladium (Pd),silver (Ag), magnesium (Mg), gold (Au), nickel (Ni), neodymium (Nd),iridium (Ir), chromium (Cr), lithium (Li), calcium (Ca), molybdenum(Mo), titanium (Ti), tungsten (W), and/or copper (Cu).

In the present embodiment, the second metal layer 16 includes Al. Inaddition, the second metal layer 16 may include a plurality of metallayers, for example, fourth, fifth, and sixth metal layers 16 a, 16 b,and 16 c. In the present embodiment, the second metal layer 16 may havea three-layer structure (Mo/Al/Mo) in which the sixth metal layer 16 cis formed on a top surface of the fifth metal layer 16 b and the fourthmetal layer 16 a is formed on a bottom surface of the fifth metal layer16 b, wherein the fifth metal layer 16 b is formed of Al or Al alloy andthe fourth and sixth metal layers 16 a and 16 c are each formed of Mo orMo alloy. However, the second metal layer 16 is not limited to theexample described above, and may be formed of various suitable materialsand to have various suitable layers.

As described above, since the first metal layer 14 is formed of analuminum alloy, the stacked structure of the first metal layer 14, thefirst transparent conductive layer 15, and the second metal layer 16 maybe simply patterned. As a result, etched surfaces on all sides of eachof the first metal layer 14, the first transparent conductive layer 15,and the second metal layer 16 are the same as one another.

The stacked structure of the first metal layer 14, the first transparentconductive layer 15, and the second metal layer 16 may be patterned bybeing simultaneously or commonly or concurrently etched using a singleetchant. Alternatively, the second metal layer 16 may be first wetetched, the first transparent conductive layer 15 may be wet etched ordry etched, and the second metal layer 16 may be then dry etched.

As described above, the first metal layer 14 formed as asemi-transmissive reflective layer may be simply patterned. Thus, themanufacturing process of the organic light-emitting display device maybe enhanced.

Referring to FIG. 5, a second photo-resist P2 is coated on the secondmetal layer 16, and a second mask process is performed using a secondphotomask M2 including a light-blocking portion M21 and alight-transmitting portion M22. Referring to FIG. 6, as a result of thesecond mask process, the first metal layer 14, the first transparentconductive layer 15, and the second metal layer 16 are patterned asfirst, second, and third pixel electrodes 114, 115, and 116,respectively, first, second, and third gate electrodes 214, 215, and216, respectively, of the thin film transistor, and first, second, andthird upper electrodes 314, 315, and 316, respectively, of thecapacitor.

Referring to FIG. 7, the active layer 212 is doped with ion impuritiesby using the first, second, and third gate electrodes 214, 215, and 216formed as a result of the second mask process as self-aligned masks. Asa result, the active layer 212 includes source and drain regions 212 aand 212 b that are doped with the ion impurities and a channel region212 c disposed therebetween. That is, by using the first, second, andthird gate electrodes 214, 215, and 216 as self-aligned masks, thesource and drain regions 212 a and 212 b may be formed without using aseparate photomask.

Referring to FIG. 8, a second insulating layer 17 and a thirdphoto-resist P3 are coated on the structure obtained as a result of thesecond mask process, and a third mask process is performed using a thirdphotomask M3 including a light-blocking portion M31 and alight-transmitting portion M32. Referring to FIG. 9, as a result of thethird mask process, a first opening 117 a and a second opening 117 b forexposing portions of the third pixel electrode 116, contact holes 217 aand 217 b that respectively expose the source and drain regions 212 aand 212 b of the thin film transistor, and a third opening 317 forexposing portions of the third upper electrode 316 of the capacitor areformed in the second insulating layer 17.

Referring to FIG. 10, a third metal layer 18 is formed on the resultingstructure of FIG. 9. The third metal layer 18 may include Al, Pt, Pd,Ag, Mg, Au, Ni, Nd, Ir, chromium (Cr), Li, Ca, Mo, Ti, W, and/or Cu. Inthe present embodiment, the third metal layer 18 includes Al.

In addition, the third metal layer 18 may include a plurality of metallayers, for example, seventh, eighth, and ninth metal layers 18 a, 18 b,and 18 c. In the present embodiment, like the second metal layer 16, thethird metal layer 18 may have a three-layer structure (Mo/Al/Mo) inwhich the ninth metal layer 18 c is formed on a top surface of theeighth metal layer 18 b and the seventh metal layer 18 a is formed on abottom surface of the eighth metal layer 18 b, wherein the eighth metallayer 18 b is formed of Al or Al alloy and the seventh and ninth metallayers 18 a and 18 c are each formed of Mo or Mo alloy. However, thethird metal layer 18 is not limited to the example described above, andmay be formed of various suitable materials and formed to have varioussuitable layers. For example, the third metal layer 18 may have athree-layer structure including a Ti layer, an Al layer, and a Ti layer.

Referring to FIG. 11, a fourth photo-resist P4 is coated on the thirdmetal layer 18, and a fourth mask process is performed using a fourthphotomask M4 including a light-blocking portion M41 and alight-transmitting portion M42. The third metal layer 18 is patterned inthe fourth mask process. In this regard, when the third metal layer 18is etched, portions of the second metal layer 16 formed below the thirdmetal layer 18 may also be patterned.

That is, referring to FIG. 12, the third metal layer 18 is patterned toform source and drain electrodes 218 a and 218 b that are respectivelyelectrically connected to the source and drain regions 212 a and 212 b.In this patterning process, a portion of the third pixel electrode 116exposed via the first opening 117 a and the third upper electrode 316exposed via the third opening 317 are simultaneously or commonly orconcurrently etched and removed. As a result, the second pixel electrode115 and the second upper electrode 315 are respectively exposed via thefirst opening 117 a and the third opening 317.

Referring to FIG. 13, the structure obtained as a result of the fourthmask process is doped with ion impurities. The doped ion impurities areB ions and/or P ions, and the doping concentration of the ion impuritiesis 1×10¹⁵ atoms/cm² or greater, and the doping process is performed,targeting the lower electrode 312 of the capacitor, which is formed bypatterning the semiconductor layer 12. Accordingly, the lower electrode312 of the capacitor becomes highly conductive, thereby forming ametal-insulator-metal (MIM) capacitor together with the first upperelectrode 314 and the second upper electrode 315, which may result inincreasing the capacitance of the capacitor.

Referring to FIG. 14, a fifth photo-resist P5 is coated on the resultingstructure of FIG. 13, and a fifth mask process is performed using afifth photomask M5 including a light-blocking portion M51 and alight-transmitting portion M52. In this regard, the exposure device isused to perform an exposing process using the fifth photomask M5,followed by developing and ashing processes. As illustrated in FIG. 15,a fourth opening 119 for exposing the second pixel electrode 115 isformed in the fifth photo-resist P5, and the remaining portion of thefifth photo-resist P5 is then sintered and formed as a third insulatinglayer 19. The fifth mask process is not limited to the example describedabove, and may be performed by forming the third insulating layer 19using an organic material and/or an inorganic material, coating thefifth photo-resist P5 on the third insulating layer 19, and performing ageneral mask process thereon to form the fourth opening 119.

Since the first pixel electrode 114, including a semi-transmissivemirror, is disposed below the second pixel electrode 115 exposed via thefourth opening 119, the first pixel electrode 114 may partially transmitlight and partially reflect light. By using the first pixel electrode114, which is a semi-transmissive mirror capable of partiallytransmitting and reflecting light, an organic light-emitting displaydevice employing an optical resonance structure may be manufactured. Inthe present embodiment, since the first pixel electrode 114, which actsas a semi-transmissive mirror, is formed of an aluminum alloy, the firstpixel electrode 114 and the second pixel electrode 115 may besimultaneously or commonly or concurrently patterned and thus, themanufacturing process of the organic light-emitting display device maybe enhanced.

Referring to FIG. 16, an organic layer 21, including an organic emissionlayer 21 a, and a counter electrode 22 are formed on the second pixelelectrode 115. The organic emission layer 21 a may be formed of a lowmolecular weight or high molecular weight organic material.

The organic layer 21 includes a hole transport layer (HTL) and a holeinjection layer (HIL) that are sequentially stacked on the organicemission layer 21 a towards the second pixel electrode 115, and includesan electron transport layer (ETL) and an electron injection layer (EIL)that are sequentially stacked on the organic emission layer 21 a towardsthe counter electrode 22. The organic layer 21 may further includevarious other suitable layers, if necessary. The organic layer 21,including the organic emission layer 21 a, may realize the opticalresonance structure by suitably varying the thicknesses of the organicemission layer 21 a for each pixel or the thicknesses of the otherlayers included in the organic layer 21 except for the organic emissionlayer 21 a.

The counter electrode 22 is formed on the organic layer 21 as a commonelectrode. In the organic light-emitting display device according to thepresent embodiment, the first pixel electrode 114 and the second pixelelectrode 115 are used as an anode, and the counter electrode 22 is usedas a cathode; however, the opposite case is also possible.

In addition, the counter electrode 22 may be formed as a reflectiveelectrode including a reflective material in order to form an opticalresonance structure. In this regard, the counter electrode 22 may beformed of Al, Ag, Mg, Li, Ca, LiF/Ca, or LiF/Al. Also, a sealing elementand an absorbent element may be further formed on the counter electrode22 to protect the organic emission layer 21 a from external moisture oroxygen.

Embodiments of the present invention may be directed to abottom-emission type organic light-emitting display device, in which thedisplayed image is realized towards the substrate 10. By having adistance between the counter electrode 22 and the first pixel electrode114 be a resonance thickness, such embodiments may also have enhancedluminous efficiency by using the optical resonance.

In addition, the lower electrode 312 of the capacitor is formed usingN+- or P+-doped polysilicon, and the first upper electrode 314 and thesecond upper electrode 315 are respectively formed using a conductivemetal and a transparent conductive material, e.g., a metal oxide,thereby forming an MIM capacitor. In contrast, when ametal-oxide-silicon (MOS) capacitor is used, a high voltage needs to becontinuously applied to a specific wiring of a panel, and thus there isa large risk of electrical shortage. However, as described above, theorganic light-emitting display device includes the MIM capacitor andthus, these problems may be prevented or reduced, and limitations on thedesign of the organic light-emitting display device are decreased.

The organic light-emitting display device and the method ofmanufacturing the same as described above provide the following effects.First, a pixel electrode employs a semi-transmissive mirror, therebyforming optical resonance in a bottom-emission type organiclight-emitting display device in which the displayed image is realizedtowards a pixel electrode. Thus, the luminous efficiency of the organiclight-emitting display device may be enhanced.

Second, the semi-transmissive mirror is formed of an aluminum alloy,thereby reducing or preventing the damage of a transparent conductivelayer or a gate electrode in a patterning process of the pixelelectrode. In addition, this allows patterning a plurality of stackedstructures of the pixel electrode in a single process. Thus, themanufacturing process of the organic light-emitting display device maybe enhanced.

Third, the organic light-emitting display device including thesemi-transmissive mirror may be manufactured by five mask processes.Fourth, an MIM capacitor structure may be formed in a simple process andthus, the manufacturing process and circuit characteristics thereof maybe enhanced.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims, andequivalents thereof.

What is claimed is:
 1. A method of manufacturing an organiclight-emitting display device, the method comprising: performing a firstmask process for forming a semiconductor layer on a substrate andpatterning the semiconductor layer as an active layer of a thin filmtransistor and a lower electrode of a capacitor; performing a secondmask process for forming a first insulating layer on the substrate tocover the active layer and the lower electrode, sequentially stacking afirst metal layer, a first transparent conductive layer, and a secondmetal layer on the first insulating layer, and then patterning the firstmetal layer, the first transparent conductive layer, and the secondmetal layer as a pixel electrode comprising a first pixel electrode, asecond pixel electrode, and a third pixel electrode that aresequentially stacked, as a gate electrode of the thin film transistorcomprising a first gate electrode, a second gate electrode, and a thirdgate electrode that are sequentially stacked, and as an upper electrodeof the capacitor comprising a first upper electrode, a second upperelectrode, and a third upper electrode that are sequentially stacked;performing a third mask process for forming a second insulating layer onthe first insulating layer to cover the pixel electrode, the gateelectrode, and the upper electrode, and patterning the second insulatinglayer to have first and second openings that expose the third pixelelectrode, contact holes that respectively expose source and drainregions of the active layer, and a third opening exposing the thirdupper electrode; performing a fourth mask process for forming a thirdmetal layer on the second insulating layer to cover exposed portions viathe first, second, and third openings and the contact holes, andpatterning the third metal layer as source and drain electrodes; andperforming a fifth mask process for forming a third insulating layer onthe second insulating layer to cover the source and drain electrodes,and patterning the third insulating layer to have a fourth openingexposing the pixel electrode.
 2. The method of claim 1, wherein, afterthe performing of the second mask process, the method further comprisingdoping the source and drain regions with ion impurities by using thefirst, second, and third gate electrodes as masks.
 3. The method ofclaim 1, wherein the performing of the fourth mask process comprisesremoving a portion of the third pixel electrode exposed via the firstopening and the third upper electrode exposed via the third opening. 4.The method of claim 2, wherein the performing of the fourth mask processcomprises removing the third upper electrode exposed via the thirdopening, and wherein, after the performing of the fourth mask process,the method further comprising doping ion impurities into the lowerelectrode from the second upper electrode exposed via the third opening.5. The method of claim 1, wherein the first metal layer comprises analuminum alloy.
 6. The method of claim 5, wherein the aluminum alloyfurther comprises nickel.
 7. The method of claim 5, wherein the firstmetal layer has a thickness in a range of 50 to 200 Å.
 8. The method ofclaim 1, wherein the first transparent conductive layer comprises amaterial selected from the group consisting of indium tin oxide (ITO),indium zinc oxide (IZO), zinc oxide (ZnO), indium oxide (In₂O₃), indiumgallium oxide (IGO), aluminum zinc oxide (AZO), and combinationsthereof.
 9. The method of claim 1, wherein the second metal layercomprises a metal selected from the group consisting of aluminum (Al),platinum (Pt), palladium (Pd), silver (Ag), magnesium (Mg), gold (Au),nickel (Ni), neodymium (Nd), iridium (Ir), chromium (Cr), lithium (Li),calcium (Ca), molybdenum (Mo), titanium (Ti), tungsten (W), copper (Cu),and combinations thereof.